Cable television (or Satellite, Internet or other media) streams can generally be classified by the presence of conditional access (CA) functions, the behavior of the virtual channel table (VCT), and whether so called “trick play” (video tape playback-like functions such as pause and fast forward) are enabled. TABLE 1 below breaks out this categorization.
TABLE 1Linear = (Static VCT)Subscription = (Static VCT + CA)IPPV = (Static VCT + CA)Switched Digital = (Dynamic VCT)VOD = (Dynamic VCT + CA + Trick Play)
Switched digital programming takes advantage of the statistics of program viewership to provide a greater selection of programming possibilities, with the associated disadvantage that certain programming may not be available if all of the network's bandwidth is occupied. But under this scenario, the bandwidth is usually better utilized since all channels being broadcast are generally being watched.
Unfortunately, unidirectional digital cable receivers (UDCR) currently cannot support switched digital programming since switched digital programming uses a dynamically changing virtual channel table (VCT) to provide relevant tuning information to the receiver device. Moreover, as switched digital services become more widespread, UDCR receivers may only be enabled to receive progressively smaller portions of the programming available on a given cable network. This means that a stored VCT may be outdated and the logical channels may not be accurately reflected (i.e., the frequency and MPEG service ID parameters appearing in the VCT may be wrong) if a UDCR simply tunes a virtual channel as described in the VCT. Only interactive Digital Cable Ready (iDCR) compliant receivers can be used in such environments—contributing substantially to the cost, and making UDCR devices unsuitable for use in receiving the switched digital programming. This leaves lower cost alternatives to have only very limited functionality in such an environment.